1. Field of the Invention
The invention relates to the interconnection of electronic components, and especially applies in flip-chip type hybridizations.
2. Description of Related Art
“Flip-chip” hybridization or “face-to-face” hybridization generally comprises forming two electronic circuits independently from each other, and placing them one on top of the other by means of interconnects both ensuring the positive mechanical connection function and the electric connection function. For example, an imager comprises, on the one hand, an array detection circuit comprising an array of photosites sensitive to electromagnetic radiation and, on the other hand, a circuit comprising electronics for reading the array of photosites. The two circuits are usually manufactured independently from each other, and then hybridized.
The first flip-chip hybridization comprised hybridizing circuits by means of solder balls, usually made of indium which, once solid, would positively connect the circuits together while forming electric connections. This type of hybridization however does not allow a high density of connections per surface area unit, and thus imposes a limit to the miniaturization of electronic components. Further, a step of heating under a reducing atmosphere is necessary during the hybridization to melt the solder balls, thereby preventing the use of materials or electronic components which cannot withstand such a heating.
Finally, the hybridization by means of a soldering is definitive since it requires creating intermetallic compounds between the solder material and the material having the soldering performed thereon. The material having the soldering performed thereon is thus modified and cannot be used twice. Part of the solder is further consumed, making a separation and resoldering impossible without losing quality. The definitive character of the soldering is strongly limiting in terms of quality control and of defective circuit repair. Thus, for example, to test the operation of the imager detection circuit, it is necessary to couple it with a read circuit. Since this coupling is performed by soldering, the read circuit in charge of the test is thus necessarily the final read circuit. As a result, if the detection circuit appears to be defective, the read circuit is also rejected since it is permanently coupled thereto, even though it would be perfectly operable. Similarly, in case of a failure of one or the other of the circuits, replacing the defective circuit is impossible. The hybrid assembly is then rejected, thus including the circuit still in perfect operating condition.
More recently, an alternative to solder balls, schematically illustrated in FIG. 1 and described in document FR 2936359, provides the forming of male and female cylindrical inserts 10 and 12 on surfaces of a first and of a second circuit 14, 16, and the placing of first circuit 14 on second circuit 16 by insertion of male insert 10 into female insert 14.
Although the manufacturing of such inserts is possible with a high surface area density due to the techniques used, this solution is in practice poorly viable. Indeed, male insert 10 and female insert 12 should form together a reliable electric connection, which thus means that the external diameter of male insert 10 is substantially equal to the intern al diameter of female insert 12 for their surfaces to be in contact. The insert manufacturing process should thus be extremely precise, just as the process of insert alignment for the insertion of the male insert into the female insert.
Document JP 01226160 provides a similar interconnection, the main difference being that the male insert is solid and has an external diameter selected to obtain a force-fitting into the female insert with a resilient and plastic deformation thereof. Here again, this requires a very high precision in manufacturing and alignment processes. Further, due to the materials used, that is, metals to obtain an electric connection, the deformation of the female insert is non-reversible. Indeed, the male and female inserts are interconnected by force-fitting by using a plastic deformation of the materials, and thus an irreversible deformation thereof. Once hybridized, it is thus no longer possible to separate the two circuits without causing the destruction of the female elements.
To overcome these problems, it is possible to fill the female insert with a solder material 20, as illustrated in FIG. 2 and described in document FR 2936359. Thereby, solder material 20 forms an electric joint between male insert 12 and female insert 14, thus enabling to slacken the constraints relative to their manufacturing or alignment precision.
The reintroduction of a solder material in the circuit interconnection however brings about disadvantages inherent to this type of hybridization, that is, the need for a heating, as well as the definitive aspect of the hybridization, as previously explained.